Fetal Adrenal Artery Doppler (FAAD) velocimetry is a promising new tool for monitoring fetal health. Therefore, establishing accurate, longitudinal reference ranges for this vessel is crucial for clinical application. The new research, conducted in Norway, provides a robust dataset for Pulsatility Index (PI), Peak Systolic Velocity (PSV), Time-Averaged Maximum Velocity (TAmax), and End-Diastolic Velocity (EDV). These ranges cover the fetal inferior adrenal artery (IAA) across the second half of gestation in low-risk singleton pregnancies.
New Fetal Adrenal Artery Doppler Reference Ranges
Scientists performed a prospective longitudinal cohort study on 146 low-risk pregnant women. Participants were examined every four weeks between 19 and 41 weeks’ gestation. The inferior adrenal artery was targeted. This is because animal studies showed increased blood flow to the fetal adrenal glands during placental dysfunction. This increased flow is a compensatory mechanism, similar to the “brain-sparing effect”. Successfully measuring blood velocity parameters in the IAA occurred in 89% of examinations. Researchers used mixed linear models to construct the longitudinal reference ranges from this large dataset.
The Pulsatility Index (PI) of the IAA showed a slight increase during the second trimester. However, it subsequently declined towards term. Furthermore, the Peak Systolic Velocity (PSV) remained stable throughout the second trimester. PSV then exhibited an increase beginning at 30 weeks’ gestation, continuing until the end of the third trimester. These distinct changes in Doppler indices are vital for clinical interpretation, helping to differentiate normal physiological changes from pathological compromise. Another study examining IAA Doppler parameters found similar results, noting a reduction in resistance around 35 weeks of gestation.
Clinical Implications for Fetal Hemodynamics
The established reference ranges for Fetal Adrenal Artery Doppler indices facilitate calculating individualized conditional reference ranges for serial measurements. Consequently, doctors can track a fetus’s growth trajectory and identify deviations with greater precision. This method provides a powerful new tool in the surveillance of fetal compromise, complementing established umbilical and middle cerebral artery Doppler measurements. Assessing adrenal blood flow is especially significant. The adrenal gland, like the brain, receives redirected blood flow during hypoxemia, a key feature of placental insufficiency. Therefore, this new approach could lead to earlier detection and better management of at-risk pregnancies, ultimately improving perinatal outcomes.
Frequently Asked Questions
Q1: Why is blood flow to the fetal adrenal artery important in placental dysfunction?
During placental insufficiency and subsequent fetal hypoxemia, the fetus adapts by redistributing blood flow to protect vital organs like the brain, heart, and adrenal glands. This “brain-sparing” effect includes increased perfusion of the adrenal glands, which is detectable as changes in Doppler blood velocity parameters like PI and PSV.
Q2: What is the main finding regarding the Pulsatility Index (PI) of the inferior adrenal artery (IAA)?
The study found that the PI of the fetal inferior adrenal artery slightly increased throughout the second trimester and then declined as the pregnancy approached term.
Q3: How were the reference ranges for the IAA Doppler parameters established?
A prospective longitudinal cohort study was conducted on 146 low-risk singleton pregnancies. Researchers used mixed linear models to analyze 542 successful examinations performed every four weeks from 19 to 41 weeks’ gestation, establishing the reference ranges for PI, PSV, TAmax, and EDV.
References
- Bergøy Ø et al. Longitudinal reference ranges for Doppler blood velocity parameters of inferior adrenal artery in the human fetus. Ultrasound Obstet Gynecol. 2026 Jan 05. doi: 10.1002/uog.70150. PMID: 41489412.
- Zhao M et al. Zone-specific reference ranges of fetal adrenal artery Doppler indices: a longitudinal study. BMC Pregnancy Childbirth. 2020 Dec 11;20(1):755.
- Ultrasound visualization and blood flow velocity measurements of the adrenal arteries in the fetus. PMC.
- Placental Insufficiency. StatPearls – NCBI Bookshelf.